Semiconductor device and method for making the same

ABSTRACT

The invention includes a semiconductor device, and a method for making the same, wherein bumps of a semiconductor chip and inner leads of a film tape carrier can be securely bonded to each other by thermal welding using a heating unit. A semiconductor wafer  50  is etched using a potassium iodide or ammonium iodide solution. By the etching, a barrier metal layer  48  is removed while the upper face of a bump  10  is simultaneously roughened and many prominences  12  are formed. The formation of the prominences  12  increases the surface area of the upper face of the bump  10  and improves the bonding between the bump  10  of the semiconductor chip and the lead of the film tape carrier.

BACKGROUND OF THE INVENTION

[0001] 1. Field of Invention The present invention relates to asemiconductor device and a method for making the same, and particularlyto a semiconductor chip mounted onto a tape substrate.

[0002] 2. Description of Related Art

[0003] In the field of semiconductor devices, tape carrier packages(TCPs) are well known as one type of bare-chip-mounted packages. FIG. 5is a schematic view of a film tape carrier. As shown in FIG. 5, the filmtape carrier 30 is generally formed by laminating a copper foil onto apolyimide resin film, forming a circuit onto the copper foil, andplating thereon using Sn or Au, as an oblong product before the productis processed together with semiconductor devices. The lead comprisesinner leads 20 bonded to an Au bump formed on an electrode pad of thesemiconductor chip, and outer leads 36 integratedly formed with theinner leads 20 and used for connection to an exterior.

[0004] A method for making a TCP by a gang bonding process whichsimultaneously bonds all bumps to inner leads will now be described withreference to FIG. 6. A semiconductor chip is placed in a positionsurrounded by a device hole 32 on a stage (not shown in the drawing),and each bump of the semiconductor chip and the corresponding inner leadare aligned so that they are exactly bonded to each other. As shown inFIG. 6(1), a heating unit 52, which is preliminarily heated to about500° C., is lowered toward the bumps and the inner leads 20 so that theheating unit 52 presses the bumps and the inner leads 20 on the stage.

[0005] The heat from the heating unit facilitates the formation of anAu/Sn eutectic alloy 46 shown in FIG. 6(2) by alloying the Au and the Snplated on the inner leads 20. The mounting of the semiconductor chip 40onto the film tape carrier 30 is completed by bonding the bumps to theinner leads 20 via the eutectic alloy 46. Next, unnecessary portions ofthe film tape carrier 30 are removed by punching to prepare a TCP.

[0006] However, the bonding of the bumps to the inner leads of thesemiconductor chip using the heating unit has the following problems.

[0007]FIG. 4 is a schematic view showing a problem which occurs duringmounting a semiconductor chip by a conventional technique. As shown inFIG. 4, a bump 10 is formed on an electrode pad 42 of a semiconductorchip 40. Since the periphery of the electrode pad 42 is covered by apassivation film 44 and protrudes, the bump 10 formed on the passivationfilm 44 also protrudes at the periphery and has an indented flat surfacein the central portion. When the inner lead 20 is put into contact withthe bump 10, a gap 18 is formed between the bump 10 and the inner lead20 due to the protrusion. Thus, the central portion of the bump 10 doesnot contribute to the bonding of the bump 10 to the inner lead 20, inthis state.

[0008] With reference to FIG. 6(2), in conventional thermal weldingbetween the bump 10 and the inner lead 20, a high load and a hightemperature are applied by the heating unit so that the Au/Sn eutecticalloy 46 is also formed in the central portion of the bump 10.

[0009] However, the application of the high load and the hightemperature causes deforming and cracking of the inner lead and crackingof the passivation film. Such phenomena result in unreliability of thesemiconductor devices as a product. Other problems, such as gasevolution from the film tape carrier and a shortened life of the heatingunit, also arise.

[0010] Accordingly, it is an object of the present invention to providea semiconductor device and a method for making the same in which bumpsof a semiconductor chip and leads of a tape substrate can be securelybonded to each other by thermal welding using a heating unit.

SUMMARY OF THE INVENTION

[0011] The present invention includes a semiconductor device thatincludes a tape substrate provided with a lead, and a semiconductor chipmounted onto the tape substrate by thermal welding a bump formed on anactive face of the semiconductor chip with the lead. The upper face ofthe bump is roughened.

[0012] In the present invention having such a configuration, the upperface of the bump is roughened so that the surface area increasescompared to a case of a flat upper face of the bump. Thus, the areacontributing to the formation of an Au/Sn eutectic alloy increases andthe melted eutectic alloy penetrates the gap between prominences by acapillary phenomenon, ensuring bonding between the bump and the lead.Thus, high load and high temperature are not required for bonding, andthe occurrence of inner lead cracking can be prevented.

[0013] In accordance with the above semiconductor device, prominenceshaving a height of 1 to 5 μm are continuously formed on the upper faceof the bump.

[0014] In the present invention having such a configuration, the heightof the prominences formed by roughening the upper face of the bump iscontrolled within a range which increases the surface area of the upperface of the bump so as to contribute to the formation of the Au/Sneutectic alloy and to ensure sufficient bonding strength between thebump and the lead. Thus, thermal welding between the bump and the leadare ensured.

[0015] It is preferable that the heights of the prominences on the upperface of the bump be the same so that the prominences securely come intocontact with the lead to facilitate the formation of the Au/Sn eutecticalloy between the prominences and the lead.

[0016] A method for making a semiconductor device that includes a tapesubstrate provided with a lead, and a semiconductor chip mounted ontothe tape substrate by thermal welding a bump formed on an active face ofthe semiconductor chip with the lead, includes the steps of rougheningthe upper face of the bump, and thermally welding the bump to the lead.

[0017] In the present invention having such a configuration, the bumpand the lead are thermally welded after the upper face of the bump isroughened. Thus, the surface area can be increased compared to a case ofa flat upper face of the bump. Thus, reliability of bonding between thebump and the lead can be enhanced.

[0018] In accordance with the above method for making a semiconductordevice, the step for roughening is performed while a barrier metalformed on a semiconductor wafer provided with the semiconductor chip issimultaneously removed.

[0019] In the present invention having a such a configuration, theroughening step and the step for removing the barrier metal in the waferprocess are simultaneously performed, and no additional process isrequired for roughening.

[0020] In accordance with the method for making a semiconductor device,the roughening treatment is performed by etching the upper face of thebump with an iodide compound.

[0021] In the present invention having a such a configuration, softetching of the upper face of the bump is facilitated.

[0022] In accordance with the method for making a semiconductor device,the iodine compound is potassium iodide or ammonium iodide.

[0023] In the present invention having such a configuration, desiredprojections can be readily formed on the upper face of the bump.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 includes illustrative views of a method for making asemiconductor device in accordance with an embodiment of the presentinvention, wherein FIG. 1(1) is an illustrative view of thesemiconductor chip before roughening a bump of a semiconductor chip, andFIG. 1(2) is an illustrative view after roughening.

[0025]FIG. 2 is an illustrative view of a bump after rougheningtreatment.

[0026]FIG. 3 is an illustrative chart showing the relationship betweenthe height of the prominence and the bonding strength of the bump andthe inner lead.

[0027]FIG. 4 is a schematic view showing a problem which occurs duringmounting of a semiconductor chip by a conventional technique.

[0028]FIG. 5 is a schematic view of a film tape carrier.

[0029]FIG. 6 includes illustrative views of a method for thermallywelding a bump of a semiconductor chip to an inner lead of a film tapecarrier, wherein FIG. 6(1) is an illustrative view of a state of thebump and the inner lead before thermal welding, and FIG. 6(2) is anillustrative view of a state of the bump and the inner lead afterthermal welding.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0030] The semiconductor device and the method for making the same inaccordance with the present invention will now be described in detailbased on the preferred embodiments with reference to the attacheddrawings. Parts corresponding to the parts described in the aboveconventional technology are referred to as the same reference numerals,and the description for these parts will be omitted. Moreover,descriptions, which are the same as those in the above conventionaltechnology, will be simplified.

[0031]FIG. 1 includes illustrative views of a method for making asemiconductor device in accordance with an embodiment of the presentinvention, wherein FIG. 1(1) is an illustrative view of thesemiconductor chip before roughening a bump of a semiconductor chip, andFIG. 1(2) is an illustrative view after roughening. Moreover, FIG. 2 isan illustrative view of a bump after roughening treatment. FIG. 3 is anillustrative chart showing the relationship between the height of theprominence and the bonding strength of the bump and the inner lead.

[0032] In this embodiment, prominences are formed on the upper face ofthe bump to increase the surface area of the upper face so that theAu/Sn eutectic alloy is readily formed by thermal welding using a gangbonding apparatus.

[0033]FIG. 1(1) shows a halfway stage of the wafer process. Apassivation film 44 is formed on a semiconductor wafer 50 that isprovided with a semiconductor chip in a region other than an electrodepad 42. A barrier metal layer 48 is formed over the passivation film 44and the electrode pad 42 above the entire semiconductor wafer 50. Thebarrier metal layer 48 includes two sub-layers. That is, a TiW sub-layer48 a is formed by sputtering on the passivation film 44, and then an Ausub-layer 48 b is formed by plating on the TiW sub-layer 48 a.

[0034] Next, a bump 10 is formed on the electrode pad 42. The bump 10 isformed by applying a photoresist on the entire surface of thesemiconductor wafer 50, and by removing the photoresist in abump-forming portion by exposure and development to form an opening, andthen by plating Au in the opening. The upper face of the bump 10 in thisstage is slightly indented in the central portion, as described abovewith reference to FIG. 3.

[0035] In this embodiment, the semiconductor wafer 50 is etched using apotassium iodide or ammonium iodide solution. The etching, as shown inFIG. 1(2), removes the barrier metal layer 48 and roughens the upperface of the bump 10 to form many prominences 12. The surface area of thebump 10 significantly increases compared to the surface area beforeetching. The difference in height between the periphery and the centralportion of the bump 10 is considerably decreased due to the formation ofthe prominences 12.

[0036] When the bump 10 and the inner lead 20 are thermally welded usingthe heating unit 52, as shown in FIG. 6(1), the area contributing to theformation of the Au/Sn eutectic alloy significantly increases, and theformation of the eutectic alloy is facilitated. In addition, the melteutectic alloy penetrates the gap of the prominences 12 by a capillaryphenomenon and adheres onto sloping faces 14 of the prominences 12 so asto enhance the bonding between the bump 10 and the inner lead 20. Thus,the bonding between the bump 10 and the inner lead 20 can be ensuredeven if the heating unit 52 is set at a lower temperature compared toconventional temperatures. Moreover, the difference in the height on theupper face of the bump 10 is considerably decreased. Hence, the pressureof the heating unit 52 can be reduced compared to the conventionalcases.

[0037] The etching solution may be a solution containing an iodinecompound or any compound other than potassium iodide and ammoniumiodide, as long as the solution exhibits etching ability. Instead of Au,the bump 10 may be formed of any material, such as Ni, in which Au isadhered to the surface of the prominence. The prominences 12 may beformed by a mechanical process, if possible, for example, by pressingthe upper face of the bump 10 using a tool having an uneven surface orby buffing the upper face of the bump 10 using such a tool. According tothe mechanical process, the heights of the prominences can be controlledwithin a predetermined range, and the formation of the Au/Sn eutecticalloy is further facilitated for the reasons described below.

[0038] The height of the prominence 12 depends on the type of theetching solution used and the etching time. As shown in FIG. 2,individual heights are also different, as shown by the lowest prominence12 a and the highest prominence 12 b. It is preferable that thedifference in the height be small as much as possible, because theformation of the An/Sn eutectic alloy is promoted in proportion to thecontact area during thermal welding between the bump and the inner lead.In the case of a large difference in the height of the prominences 12,prominences having lower heights are still distant from the inner leadand thus do not contribute to the formation of the Au/Sn eutectic alloy,even when the inner lead is pressed by the heating unit.

[0039] Experimental results have been prepared regarding the heights ofthe prominences 12, wherein the height A of the lowest prominence is 1μm or more, and the height B of the highest prominence is less than 5μm. The experimental results will now be described.

[0040] The present inventor has performed experiments regarding therelationship between the heights of the prominences and the bondingstrength of the bump and the inner lead, and has obtained the dataconfirming the effects. The results will now be described based on FIG.3.

[0041] Term 1 in the table represents the surface roughness of the bump,that is, the heights of the prominences on the upper face of the bump.The description “0 to less than 1” represents all the heights of theprominences lie within the range of 0 to 1. Term 2 represents the stateof the formation of the Au/Sn eutectic alloy, in which ◯ indicates thatthe formation is satisfactory, Δ indicates that the formation is not sosatisfactory, and X indicates that the formation is unsatisfactory. Item3 represents the bonding strength between the bump and the inner liner,in which ◯ indicates that reliable strength is obtained, Δ indicatesthat strength is slightly insufficient, and X indicates that strength isinsufficient. Item 4 represents the comprehensive determination, inwhich ◯ indicates that the reliable results are obtainable in thesemiconductor device, Δ indicates that the slightly unreliable resultsare obtainable in the semiconductor device, and X indicates that theunreliable results are obtainable in the semiconductor device.

[0042] As shown in chart, the height of the most preferable height ofthe prominence is within a range of 1 μm to less than 5 μm. A height ofthe prominence of 0 μm to less than 1 μm is not substantially differentfrom a flat face of the bump, and thus, advantages by providing theprominence are insufficient. A height of prominence of 5 μm or moreresults in a large distance between the base portion of the prominenceand the inner lead. Thus, the melted Au/Sn eutectic alloy is not adheredto the vicinity of the base portion of the prominence and will notcontribute to an improvement in bonding strength.

[0043] As described above, in the semiconductor device and the methodfor making the same in accordance with the embodiments of the presentinvention, the upper face of the bump of the semiconductor chip isroughened to form prominences. If the temperature and the pressure ofthe heating unit are set to be lower than those in conventionalprocesses, sufficient bonding strength is achieved between the bump andthe inner lead. Since the removal of the barrier metal and theroughening of the upper face of the bump are simultaneously performed,no additional step is required.

[0044] As described above, a semiconductor device in accordance with theinvention includes a tape substrate provided with a lead, and asemiconductor chip mounted onto the tape substrate by thermal welding abump formed on an active face of the semiconductor chip with the lead.Thus, reliability of the bonding between the semiconductor chip and thetape substrate can be significantly improved by a simplified treatmentin a wafer process. Accordingly, the production cost of thesemiconductor device can be reduced.

What is claimed is:
 1. A semiconductor device, comprising: a tapesubstrate provided with a lead; and a semiconductor chip that includesan active face and a bump formed on the active face, the bump having anupper face, the semiconductor chip being mounted onto the tape substrateby thermal welding the bump formed on the active face of thesemiconductor chip with the lead of the tape substrate, the upper faceof the bump being roughened.
 2. The semiconductor device according toclaim 1, wherein prominences having a height of 1 to 5 μm arecontinuously formed on the upper face of the bump.
 3. A method formaking a semiconductor device that includes a tape substrate providedwith a lead, and a semiconductor chip mounted onto the tape substrate bythermal welding a bump formed on an active face of the semiconductorchip with the lead, the method comprising the steps of: roughening anupper face of the bump; and thermally welding the bump to the lead. 4.The method for making a semiconductor device according to claim 3,wherein the roughening step is performed while a barrier metal formed ona semiconductor wafer provided with the semiconductor chip issimultaneously removed.
 5. The method for making a semiconductor deviceaccording to claim 3, wherein the roughening step includes etching theupper face of the bump with an iodide compound.
 6. The method for makinga semiconductor device according to claim 5, wherein the iodine compoundis potassium iodide or ammonium iodide.
 7. The method for making asemiconductor device according to claim 4, wherein the roughening stepincludes etching the upper face of the bump with an iodide compound. 8.The method for making a semiconductor device according to claim 7,wherein the iodine compound is potassium iodide or ammonium iodide. 9.The semiconductor device according to claim 2, wherein each of theprominences includes sloping faces that define a substantially roundedtip.
 10. The semiconductor device according to claim 9, wherein slopingfaces of adjacent prominences define substantially rounded channels,each substantially rounded channel separating adjacent prominences. 11.The semiconductor device according to claim 1, wherein the semiconductorchip includes a semiconductor wafer.
 12. The semiconductor deviceaccording to claim 11, wherein the semiconductor chip includes apassivation film and a barrier metal layer disposed between thesemiconductor wafer and the bump.
 13. The semiconductor device accordingto claim 12, wherein the barrier metal layer includes an Au sub-layerand a TiW sub-layer.
 14. The semiconductor device according to claim 13,wherein the semiconductor chip includes an electrode pad disposedbetween the semiconductor wafer and the barrier metal layer.
 15. Thesemiconductor device according to claim 14, wherein the barrier metallayer is only disposed between the bump and the semiconductor wafer soas not to project laterally from the bump.